JPH10206880A - Liquid crystal display element and driving method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflection type liq. crystal display which is very bright and has high contrast. SOLUTION: The liq. crystal panel 8, in which a first liq. crystal layer 6 is inserted between a substrate 4 formed of a transparent electrode film 2 consisting of an interference filer 1 for reflecting blue color and indium tin oxide(ITO) and a substrate 5 formed of a transparent electrode film 3 consisting of indium tin oxide(ITO), is formed on a glass. Then, three sheets of liq. crystal panels; a liq. crystal panel 12 in which similarly, a green interference filter 10 is provided and a second liq. crystal layer 11 is inserted between substrates and a liq. crystal panel 22 in which a third liq. crystal layer 21 is inserted between an aluminum reflection film 20 and an ITO layer 3; are superimposed together. As a result, the interference filters and the liq. crystal layers are multilayered to enable the separation of color without absorption.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a bright liquid crystal display device capable of performing a reflection type full color display and a driving method thereof.

[0002]

2. Description of the Related Art A display device using a nematic liquid crystal has several modes depending on the orientation of liquid crystal molecules. The most widespread is a twisted nematic (TN) liquid crystal, and there are also a homeotropic (vertical) orientation or a homogeneous (horizontal) orientation birefringence mode, a guest-host mode, and the like.

The above-mentioned TN liquid crystal is a state in which a liquid crystal having a positive dielectric anisotropy is twisted 90 degrees between substrates with electrodes which have been subjected to horizontal alignment processing, and is in a stable state. When the wavefront is rotated by 90 degrees and the polarizer and the analyzer are orthogonal to each other, white display is obtained. On the other hand, when the liquid crystal molecules rise by application of a voltage, the incident polarized light travels through the liquid crystal layer as it is, so that it is absorbed by the analyzer and black display is performed.

[0004] When color display is performed using the above TN liquid crystal, micro color filters of three colors of red, green and blue are provided on three adjacent pixels to perform additive color mixing. Generally, the transmittance of the above color filter is low,
Since the N liquid crystal and the birefringent mode liquid crystal require a polarizing plate that absorbs one polarized light, the overall transmittance is 10% or less. Therefore, there is only a transmission type using a backlight for color display, and a reflection type liquid crystal using external light is impossible.

On the other hand, there are conventional examples in which a guest-host mode using a dichroic dye is used to perform bright color display (for example, Japanese Patent Application Laid-Open No. 61-238024 and Japanese Patent Application Laid-Open No. 238424, etc.). This is a method in which a plurality of panels using dichroic dyes having different colors are overlapped to perform multicolor display by subtractive color mixture. The first panel is blue, the second panel is green, the third panel is black if it absorbs red light, and if any panel does not absorb it, it is colored. If not absorbed, a white display is obtained.

[0006]

As described above, the mode using a polarizing plate has a low light utilization factor, and in particular, only a reflection type can provide a dark display, so that color display is difficult. In the method using, there is a correlation that as the contrast is increased, the image becomes darker, and it is difficult to realize a display with a very high contrast while maintaining the brightness.

Accordingly, an object of the present invention is to realize a very bright and high-contrast reflective liquid crystal display.

[0008]

In order to solve the above-mentioned problems, a liquid crystal display device of the present invention comprises a first liquid crystal sandwiched between electrode films and stacked in a thickness direction between a polarizing plate and a reflection film. Layers, a second liquid crystal layer and a third liquid crystal layer, and red, blue, and blue provided between the first liquid crystal layer and the second liquid crystal layer closest to the polarizing plate among the three liquid crystal layers. A first selective reflection film that reflects light of one of green and transmits light of another color; and a first selective reflection film provided between the second liquid crystal layer and the third liquid crystal layer. And a second selective reflection film that reflects light of one color and transmits light of another color.

Preferably, the selective reflection film comprises an interference filter comprising a multilayer film or a film in which two kinds of chiral nematic liquid crystals having a predetermined twist pitch and opposite twist directions are dispersed in a polymer matrix. It is characterized by the following.

With the above configuration, the liquid crystal display device of the present invention can be used in a specific wavelength band in the case of an interference filter made of an inorganic multilayer film or a circular dichroism exhibited by a chiral nematic liquid crystal having a short twist pitch. As a result, a very bright and high-contrast reflective liquid crystal display can be realized by utilizing the selective reflectivity in which the light is reflected and the other wavelength bands are transmitted.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a liquid crystal display device and a method of driving the same according to an embodiment of the present invention will be described in detail with reference to the drawings.

The liquid crystal display element of the present invention comprises three liquid crystal layers stacked in the thickness direction between a polarizing plate and a reflective film,
Each of the three liquid crystal layers is sandwiched between electrode films. Of the three liquid crystal layers, a red, blue, and green color liquid crystal layer is provided between a first liquid crystal layer closest to the polarizing plate and a second intermediate liquid crystal layer. A first selective reflection film that reflects light of one of the colors and transmits light of another color, and any one of the other colors is disposed between the second and third liquid crystal layers; , And a second selective reflection film that reflects light of another color and transmits light of another color.

That is, the liquid crystal display element of the present invention uses an interference filter instead of a commonly used color filter.

Therefore, the above-mentioned interference filter will be described below. A normal color filter separates colors by absorbing light.However, in the case of an interference filter made of an inorganic multilayer film or a circular dichroism indicated by a chiral nematic liquid crystal with a short twist pitch. It has the property of selective reflection, that is, light in a specific wavelength band is reflected and other wavelength bands are transmitted.

More specifically, in the case of an interference filter, two or more inorganic films of several tens of nm having different refractive indexes are repeatedly formed, and the optical path length (refractive index × thickness) of these films is changed. The wavelength band of the selective reflection can be changed. On the other hand, in the case of a chiral nematic liquid crystal, the circularly polarized light in the twisting direction is selectively reflected at a wavelength centered on the product of the refractive index of the liquid crystal and the twisting pitch, and having a bandwidth of the product of the birefringence Δn of the liquid crystal and the twisting pitch. Is done.

By brightening the selective reflection film and the liquid crystal layer as described above, it is possible to realize a bright and high-contrast reflection-type display. explain.

First, natural light passes through the polarizing plate, and only one polarized light is transmitted, enters the first liquid crystal layer, and becomes elliptically polarized light. Of the modulated light, only the reflection color of the first selective reflection film, for example, blue elliptically polarized light is reflected, and
Is detected by the polarizing plate through the liquid crystal layer, and yellow light is transmitted. The molecules of the liquid crystal layer are oriented in the direction of 45 ° with respect to the polarizing plate, and the Δnd of the first liquid crystal layer is adjusted so as to be a (1 + 2n) / 4 wavelength plate (n is an integer) with respect to the blue wavelength. For example, when no voltage is applied, blue light passes through the liquid crystal layer on the return path and becomes linearly polarized light orthogonal to the incident light, so that it is absorbed by the polarizing plate and becomes dark, and when a voltage is applied, the birefringence of the liquid crystal layer is reduced. The incident polarized light is returned as it is, and blue light is emitted.

Next, the yellow light transmitted through the first selective reflection film is further modulated by the second liquid crystal layer, and only the green light, for example, is reflected by the second selective reflection film. Upon receiving the modulation of the second liquid crystal layer and the first liquid crystal layer, the liquid crystal returns to the polarizing plate.
Therefore, the green light receives the modulation of the sum of the birefringences of both the first and second liquid crystal layers.
If a voltage is applied to the second liquid crystal layer so that the birefringence is obtained by subtracting the amount of birefringence, the emission light intensity of green light can be controlled independently.

The red light transmitted through the second selective reflection film is
Further, the light is reflected by the reflection film through the third liquid crystal layer, and is modulated by the third to first liquid crystal layers on the return path. Therefore, similarly to the case of the second liquid crystal layer, the first and second liquid crystal layers are previously formed. The outgoing red light can be controlled by determining the applied voltage in consideration of the birefringence value of the liquid crystal layer.

As described above, bright colors can be displayed without using red, green and blue light absorbing filters.
Since one polarizing plate is used, a high contrast can be realized. In the above example, a reflective film that reflects blue is provided on the side close to the deflection plate, and then a film that reflects green is provided.However, it does not matter in what color the film is selected. , Red, blue, and green may be provided.

Next, a specific liquid crystal display device of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view of a liquid crystal display device according to an embodiment of the present invention. In FIG.
A substrate 4 on which an interference filter 1 for reflecting blue and a transparent electrode film 2 made of indium tin oxide (ITO) are formed on glass having a thickness of 0.3 mm, and indium tin oxide (ITO)
A liquid crystal panel 8 having a first liquid crystal layer 6 interposed between substrates 5 having a transparent electrode film 3 made of is formed.

Next, a green interference filter 10 is provided in the same configuration as the liquid crystal panel 8 described above, and a liquid crystal panel 12 having a second liquid crystal layer 11 sandwiched between substrates, and an aluminum reflection film 20 and an ITO Liquid crystal panel 2 sandwiching a third liquid crystal layer 21
2. The three liquid crystal panels are overlapped.

Then, a polarizing plate 30 is attached to the forefront, and a forward scattering film 29 is attached immediately behind the polarizing plate.
As the interference filter, a commercially available film obtained by depositing an inorganic multilayer film was used, and its spectral transmission characteristics are shown in FIG. Since the interference filter is a mirror surface, a forward scattering film is attached to impart a scattering property and widen the viewing angle. Without this, the viewing angle becomes extremely narrow.

The first to third liquid crystal layers were subjected to an alignment treatment such that liquid crystal molecules on one substrate were in a vertical alignment and liquid crystal molecules on the other substrate were in a horizontal alignment. Note that the orientation of the liquid crystal layer may be a homogeneous orientation or a twisted nematic, but here, a hybrid orientation is used in order to widen the viewing angle.

FIG. 3 shows the polarization axis direction 31 of the polarizing plate.
32, 33, and 34 show the directions in which the long axes of the liquid crystal molecules are aligned by the horizontal alignment processing of the third liquid crystal layer. The orientation direction 32 of the first liquid crystal layer is at 45 degrees with respect to the polarization axis 31,
The second liquid crystal layer was in a direction 33 perpendicular to the first liquid crystal, and the third liquid crystal layer was in the same direction as 32.

A fluorine-based liquid crystal mixture having a birefringence Δn of 0.0802 with respect to light having a birefringence Δn of 550 nm was injected into each of the first to third liquid crystal layers. . The Δn of the liquid crystal mixture is 0.0832 at 450 nm, which is the center wavelength of blue, and 6 n, which is the center wavelength of red.
At 10 nm, it is 0.0791. Specifically, the first liquid crystal layer is 2.7 microns, the second liquid crystal layer is 6.1 microns,
The third liquid crystal layer was set at 7.3 microns.

In the hybrid alignment, since the liquid crystal molecules are half-hung, the effective Δnd is の of the homogeneous alignment, and the birefringence of the first liquid crystal layer is 0.11.
2 microns, one quarter wavelength of 450 nm. Since the light incident on the second liquid crystal layer passes through both the first liquid crystal layer and the second liquid crystal layer, the birefringence of both must be summed up.
Since the second liquid crystal layer is oriented perpendicular to the first liquid crystal layer, the subtracted value of the two becomes effective birefringence. Therefore, when no voltage is applied, 0.0802 × (6.1-2.7) / 2 microns = 0.136 microns, which is a quarter wavelength of 550 nm. Furthermore, since the third liquid crystal layer is arranged in the same direction as the first liquid crystal layer, 0.0791 × (2.7−6.1 + 7.3)
Micron = 1.54 micron, one quarter wavelength of 610 nm.

When no voltage was applied, a bright white display with a reflectivity of 36% was obtained when the voltage was applied to all three liquid crystal panels. The contrast ratio between black and white is about 30. When displaying color, the blue component is
It is sufficient to apply a voltage substantially proportional to the blue component Yb of the pixel data as it is, but for green, as the green component Yg of the pixel data, Yg ′ = Yg − (− Yb) × (2.7 / 6.1) =
Yg + 0.443Yb was used as corrected pixel data, and a voltage corresponding thereto was applied. 0.443 is a proportionality constant consisting of the ratio of Δnd between the first and second liquid crystal layers, and Yb is given a minus sign since the orientation is orthogonal. Further, the voltage applied to the third liquid crystal layer is Yr ′ = Yr−Yg ′ × (3.4 / 7.1) = Yr with respect to the red component Yr.
−0.479 Yg ′ was used as corrected pixel data.

As described above, by correcting the pixel data with the voltage applied to the second and third liquid crystal layers, almost a desired color can be displayed and a bright color display can be achieved.

The order of the colors of the interference filters does not necessarily have to be the same as that of the present embodiment. Any one of the RGB colors is used for the first selective reflection film, and the other color is used for the second selective reflection film. What is necessary is just to reflect. Further, selective reflection of a chiral nematic liquid crystal may be used as the selective reflection film. In the present embodiment, three panels are stacked as a liquid crystal layer. However, it is better to disperse the liquid crystal layer in a polymer matrix and then stack a stretched and oriented film or a substrate as a film. This is preferable because parallax does not occur even when the pixel pitch is small.

[0032]

The liquid crystal display device of the present invention can realize a very bright and high-contrast reflective liquid crystal display by attaching a polarizing plate to a liquid crystal panel in which a selective reflection film and a liquid crystal layer are multilayered. . Further, according to the driving method of the liquid crystal display device of the present invention, it is possible to drive the intermediate color by the liquid crystal display device.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a liquid crystal display element according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating spectral characteristics of a selective reflection film of a liquid crystal display element according to an embodiment of the present invention.

FIG. 3 is a plan view of the liquid crystal display element according to the embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 interference filter 2 transparent electrode film 3 transparent electrode film 4 substrate 5 substrate 6 first liquid crystal layer 8 liquid crystal panel 10 interference filter 11 second liquid crystal layer 12 liquid crystal panel 20 reflection film 21 third liquid crystal layer 22 liquid crystal panel 29 front Scattering film 30 polarizing plate

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI G09F 9/35 320 G09F 9/35 320

Claims (5)

[Claims] A first liquid crystal layer sandwiched between electrode films and stacked in a thickness direction between a polarizing plate and a reflection film;
A second liquid crystal layer, a third liquid crystal layer, and a red, blue, and green liquid crystal layer provided between the first liquid crystal layer and the second liquid crystal layer closest to the polarizing plate among the three liquid crystal layers. A first selective reflection film that reflects light of one of the colors and transmits light of another color; and any one of the other colors provided between the second liquid crystal layer and the third liquid crystal layer. A second selective reflection film that reflects light of one color and transmits light of another color. 2. The liquid crystal display device according to claim 1, wherein a forward scattering film is provided on the deflection plate side of the first liquid crystal layer. 3. The liquid crystal display device according to claim 1, wherein the selective reflection film is an interference filter composed of a multilayer film. 4. The liquid crystal display according to claim 1, wherein the selective reflection film is formed of a film in which two kinds of chiral nematic liquid crystals having a predetermined twist pitch and opposite twist directions are dispersed in a polymer matrix. element. 5. A first liquid crystal layer sandwiched between electrode films and stacked in a thickness direction between a polarizing plate and a reflection film,
A second liquid crystal layer, a third liquid crystal layer, and a red, blue, and green liquid crystal layer provided between the first liquid crystal layer and the second liquid crystal layer closest to the polarizing plate among the three liquid crystal layers. A first selective reflection film that reflects light of one of the colors and transmits light of another color; and any one of the other colors provided between the second liquid crystal layer and the third liquid crystal layer. A method for driving a liquid crystal display element comprising: a second selective reflection film that reflects light of one color and transmits light of another color, wherein a voltage applied to the second liquid crystal layer is adjusted to one of the colors and The voltage applied to the third liquid crystal layer is set based on the calculation of the pixel data of one of the other colors.
A method for driving a liquid crystal display element, wherein the method is set based on calculation of red, blue, and green pixel data.